How photovoltaic power stations and wind turbines can complement each other

Project state

Started

Photovoltaic plants and wind turbines can mutually balance their fluctuating energy output. To this end, the researchers are developing new control schemes in the research project “PV-Wind-Symbiose”. | Image: Armin Kübelbeck, CC-BY-SA, Wikimedia Commons

In the wake of the climate-friendly restructuring of the German energy supply system, renewable energy generation systems are to increasingly replace nuclear and coal-fired power plants. In the conventional grid, these large-scale power plants provide a substantial part of the necessary reactive power for the transmission systems. If they are turned off temporarily or permanently, then decentralised systems such as wind turbines and photovoltaic systems will have to accomplish this task in their stead.

Especially renewable energy power plants directly connected to the high voltage level can make a significant contribution to grid control. This is where the project “PV-Wind-Symbiose” comes in. The project partners will carry out investigations on a real combined wind and PV power plant, if possible connected to the 110-kV grid. In collaboration with a grid operator and manufacturers of PV inverters and wind turbines, they aim to explore how reactive power could be provided and integrated into the grid beyond the existing directives governing feed-in.

Consider wind turbines and photovoltaic systems as a unity

To do this, it is first necessary to develop the reactive power capacity of PV systems and wind turbines, and to develop common rules for wind farms and PV power plants. These changes lead to a so-called virtual power plant, with which the concept can be examined in terms of system reliability, losses, harmonic emissions and cost structure, all under real conditions.

Virtual power plants: Networked small-scale plants working in conjunction

The purpose of virtual power plants is to link the energy production of smaller plants, so that grid operators can treat them as one large power plant. They usually consist of a mix of photovoltaic systems and wind turbines supplemented by biomass and hydroelectric power plants. However, geothermal plants and CHPs can also contribute their output and partake in virtual power plants.

The control centre communicates with the individual plants and determines the amount of energy required by the grid. In addition, it checks to see how much power can be supplied by volatile producers at the present time. For predictions, it relies on high-resolution weather data and combines it with local data of the producers. With this information and with price forecasts for the electricity markets, a virtual power plant can then feed in electricity.

One disadvantage is the communications overhead. It requires a lot of computing power and incurs additional costs. Nevertheless, virtual power plants could maintain a secure energy supply in the future.

Plant and grid simulations are being run concurrently with the experiments to develop suitable control algorithms and assess any effects on expanded grid areas. With this information, the researchers can finally evaluate the marketability of reactive power provided by virtual power plants. The goal is to increase the usability of PV plants and wind turbines for normal grid operation and to propose suitable technical solutions, control strategies and compensation models. This project contributes towards designing a stable and reliable grid design with 100 per cent renewable energy. This way, the security of supply during the energy transition could remain as high as it currently is in Germany.

Course of the project in detail

In the first year of the project, the scientists will select suitable wind turbines and PV power plants that are available for the project and that are expected to yield the most insightful results. The status quo is recorded metrologically and then modelled in a simulation. The following year, the project partners will model expanded grid and plant control strategies. They aim to realise the concepts that proved to be most successful in the simulations as real plants in collaboration with industry partners and grid operators. In the final year of the project, the metrological review of the impact of these changes will be carried out along with a validation of the simulations, and the development of models for pricing and appropriate compensation for additional ancillary services that a virtual power plant can provide.

The co-operation partners, Fraunhofer-Institut für Solare Energiesysteme (Fraunhofer ISE) and the Institute of High Voltage Technology and Electrical Power Systems of the Technischen Universität Braunschweig (elenia), are in continuous exchange and work closely together within the project group. The focus of elenia is on grid simulation and energy industry considerations. Fraunhofer ISE focuses on measurement and characterisation, controller development and plant simulations.